The demand in distributed power management and power-efficient alternatives is calling for a new wave of power control devices. Ready for higher level integration, these new elements include micro sensors and micro actuators to realize close-loop control of complex systems. For energy intensive applications, such as home and business appliances, lighting, solar energy and automotive, high voltage and/or high current circuit control devices play a critical role. Traditional macro-machined relays, micro electro-mechanical switches and semiconductor relays are not best suited for the aforementioned applications. In particular, inter solar panel routing, smart power measuring, and industrial lighting all require small, embeddable relays. These emerging applications currently do not have suitable products for their needs.
Electro-mechanical relays and switches are in almost every major electrical system, especially those requiring moderate power (>10 w), such as automotive, industrial, residential, commercial power, and lighting. Macro-machined and assembled electromagnetic relays are limited in miniaturization and integration. Although reliable industrial solutions, current high current contact relays are difficult to fit in a package 3000 mm3 or smaller. The design approach of traditional coil winding and contact switch assembly intrinsically limits further miniaturization.
Although truly small in size, traditional micro electro-mechanical switches have faced major challenges in high power applications (>10 W). They are difficult to design using conventional silicon technology. Silicon MEMS devices (and their close variants, such as electro-formed metal devices) generally result in closely spaced, fragile elements. Most switches use electrostatic actuation to move the switch arm into contact with the mating electrical contact. This can only be done if the switch arm is close to the actuating mechanism, and if the actuation force is small. However, for high power applications, this is unacceptable. Power coupling across the small gap between conductors is appreciable at high power, self-charging occurs at high power resulting in self-actuating switches (the “hot switch” effect), and high power applications require that high current be passed through the conducting elements, which would destroy the thin membranes.
Solid-state relays (SSR) use a small control signal, usually optically isolated, to control a larger load current or voltage. SSRs have fast switching times of the order of microseconds to milliseconds as well as lower latching current of tens of milliamps. However, the relatively higher insertion loss at “close” and the reverse leakage current at “open” both prevent SSRs from becoming the most energy efficient power management device.